1. Field of the Invention
The present invention relates to reel to reel tape control systems and, more particularly, the present invention relates to a reel to reel tape radius measurement apparatus utilizing the Hall effect output of brushless DC drive motors.
2. Discussion of Prior Art
In reel to reel tape transport systems, the radius of the tape, at any given instant, is required in the tape control system to accurately keep the tape at a constant velocity.
In the 1977 patent to Koski (4,015,799) one approach to measuring the reel radii is to utilize a supply reel tachometer coupled to the shaft of the supply reel motor and a take-up reel tachometer coupled to the shaft of the take-up motor. The outputs of the two respective tachometers are then processed by motion control logic to determine the reel radii.
The 1978 patent issued to Eige (4,125,881) sets forth a first tachometer to sense the tape motion which generates a single pulse at the completion of a revolution of the reel. The second tape motion sensor is a two-phase fine tachometer having a large number of fine graduations or lines uniformly spaced circumferentially around the tachometer. Based upon the output of the two tachometers, the reel radii can be calculated.
The present invention provides an alternative means for determining the revolution of one of the motors for determination of a full revolution without using a separate tachometer.